This invention relates to the field of sputter coating, and more particularly, to the design of the cathode and target assembly for such apparatus.
This application is related to the patent application entitled "Apparatus for Improving the Uniformity of Ion Bombardment In a Magnetron Sputtering System", Ser. No. 095,560, filed Sept. 10, 1987 which is a continuation of application Ser. No. 848,750, filed Apr. 4, 1986 and now abandoned, and of the application entitled "Method and Apparatus for Handling and Processing Wafer-Like Articles", one being Ser. No. 222,327, filed July 20, 1988, which is a continuation of application Ser. No. 112,766, filed Oct. 22, 1987, now abandoned, which is a continuation of application Ser. No. 848,687, filed Apr. 4, 1986 and now abandoned, and the other being application Ser. No. 222,328, filed July 20, 1988 which is a continuation of application Ser. No. 112,777, filed Oct. 22, 1987 now abandoned which is a continuation of application Ser. No. 848,297, filed Apr. 4, 1986 and now abandoned.
Sputtering is an important technique for applying thin films to substrate materials, such as wafers utilized in manufacturing microelectronic components. The process can best be envisioned as a series of steps, occurring in a low-pressure chamber into which a gas, typically argon, has been introduced. A negative potential is applied to a cathode structure, establishing an electric field, and electrons from the cathode collide with argon atoms, creating ions and exciting a glow discharge. Accelerated by the cathode's negative potential, the ions travel parallel to the electric field lines and impact a target, composed of the coating material, carried in the cathode structure. The kinetic energy of these ions is sufficiently high to dislodge some target surface atoms, which then condense on the substrate to form the film.
One technique used in the sputtering art has been the employment of magnetic fields to enhance the ion bombardment of the target. In such apparatus, referred to as magnetron sputtering devices, magnetic means are disposed to induce a relatively strong field in the vicinity of the target face, with the magnetic field lines oriented generally perpendicular to those of the electric field. Electrons emitted from the target face are influenced by the magnetic field so that their path of motion becomes curved, and in effect, the magnetic field "traps" such electrons in the vicinity of the target. The effect of this action is to promote electron-argon collisions close to the target face, maximizing the ion flux bombarding the target. Typical of magnetron sputtering apparatus is the device disclosed in U.S. Pat. No. 4,472,259, assigned to the assignee of the present invention.
From the perspective of the designer of sputtering apparatus, an important consequence of the ion bombardment is target heating. Ejection of a target material atom is only one result of an ion impacting the target surface, and the vast proportion of system input power appears finally as heat in the target. Thus, sputtering cathode systems are sensitive to design changes that call for increased input power, as increases in effective power (power that, for example, increases the deposition rate) entail increases in target heating.
Emerging design criteria specified by users of sputtering equipment call for power requirements that exceed the capacities of conventional apparatus. Several factors combine to produce this situation. First, users commonly specify relatively soft coating materials, such as gold, aluminum, or aluminum alloys. As discussed in more detail below, such materials present particular problems in dealing with target heating. Second, users call for higher deposition rates, to increase productivity and film quality. To achieve such rates requires equipment capable of operating at higher input power levels than are now seen in the art. And in addition, there exists a trend toward ever-larger substrates, requiring cathodes and targets larger than those heretofore produced, creating particular design problems.
These factors, and particularly the latter two, require equipment that departs from conventional designs in dealing with target heating. Yet the art has offered few innovations aimed at dealing with the problems of heat buildup. Moreover, as detailed below, conventional designs inherently limit the ability of a target to withstand the heat buildup of sustained high-power operation. Thus, it was left to the present inventors to address this problem and achieve the solution presented herein.